Ethylene/α-olefin/non-conjugated polyene copolymer rubbers, such as ethylene-propylene-diene copolymers (“EPDM”), have outstanding performance in terms of weatherability, heat resistance and ozone resistance. As a result, rubber compositions containing such copolymer rubbers, crosslinked products of the compositions, and foamed products of the compositions have been broadly used for automotive parts, industrial rubber articles, electrically insulating materials, civil engineering and construction materials. Specifically, EPDM foams (sponges) obtained by vulcanizing and foaming an EPDM rubber have been used as sealing material for a variety of industrial products.
For automobiles, sealants sealing between car body opening peripheries, and opening/closing members for openings such as doors and trunk lids are used to prevent rain, wind and sounds from the outside. The sealants commonly include a solid member attached to door frames, trunk lids, car body opening peripheries and the like, and a foamed member to seal gaps between car body opening peripheries, and opening/closing members for openings. The foamed member is required to be deformable to conform to irregularities and curved shapes of door frames, trunk lids and the like, and to have a hardness which allows close contact with door frames, trunk lids and the like.
There is now a demand for weight reduction of automobiles and, in turn, weight reduction of EPDM foams used for automotive sealants. In order to manufacture EPDM foams with low density and high sealing performance, higher double-bond content (i.e., diene content) is generally required for faster curing and higher ultimate crosslink density for improved cellular foam structure and improved mechanical properties, such as compression set. However, higher diene levels can increase the cost of EPDM rubbers. Furthermore, interpolymers containing high levels of diene can result in cured formulations with shorter scorch times, which can lead to processing problems. It has also been studied that the density of EPDM foams can be lowered by raising the foaming ratio of the EPDM foams. However, an increase in the foaming ratio of the EPDM foams can undesirably affect a number of product properties, including compression set, compression load deflection, and tear resistance, which can negatively impact the sealing performance and service life of the automotive sealants made therefrom.
U.S. Pat. No. 8,353,130 discloses a door weather strip including an attaching base part and a hollow seal part. Both the attaching base part and the seal part are made of the same EPDM sponge rubber material by an extrusion process. The door weather strip has a specific gravity that is from 0.36 to 0.44, a low stretch stress of 200 kPa to 230 kPa, and an average foaming cell diameter of 180 μm to 220 μm.
U.S. Pat. No. 8,205,391 provides an automobile weather strip which has a trim part, which has an insert member and a covering material, and a sealing part. The covering material comprises a sponge material comprising a blend of an EPDM rubber and an olefin-based thermoplastic synthetic resin where the covering material has a specific gravity of 0.6 to 0.8 and a 25%-stretching stress of 500 KPa or more. The olefin-based thermoplastic synthetic resin is described as being a polyethylene resin, a polypropylene resin, or an ethylene/octane resin.
U.S. Pat. No. 8,101,254 relates to a molded product comprising a rubber composition that comprises an ethylene/α-olefin/non-conjugated polyene copolymer (A), and a polyolefin resin (B) having an Mn of not less than 10,000 and/or an ethylene/α-olefin copolymer (C) having Mn of 2500 to 5000.
U.S. Pat. No. 7,319,121 relates to foamed thermoplastic elastomer profiles comprising a foamable thermoplastic elastomer composition having a) a cross-linkable hydrocarbon rubber and b) a thermoplastic polyolefin resin having a Tm greater than 120° C. The composition further comprises: a) 25 to 30 wt % of a partially or fully vulcanized reaction product of said cross-linkable hydrocarbon rubber with a cross-linking agent, said reaction product being present as a dispersed phase; b) 7 to 12 wt % of said thermoplastic resin as a continuous phase; c) 8-22 wt % of an elastomeric thermoplastic modifier; and, optionally, d) 3-12 wt % solid filler; and/or e) 35-45 wt % of non-aromatic hydrocarbon oil; where the composition has been prepared by dynamically vulcanizing said composition.
U.S. Pat. No. 7,326,471 provides an automotive sealant composite structure that includes (i) a first piece comprising a first elastomeric component that includes an at least partially crosslinked rubber, a first olefinic thermoplastic resin component, and a second olefinic thermoplastic resin component, and (ii) a second piece comprising a second elastomeric component that comprises a thermoset ethylene copolymer rubber and an olefinic thermoplastic resin.
U.S. Publication No. 2012/0059123 discloses a copolymer rubber composition comprising 60 to 75% by weight of a copolymer rubber (1) that is an EPDM comprising 50 to 70 mol % ethylene units and 30 to 50 mol % of α-olefin units, and 40 to 25% by weight of a copolymer rubber (2) that is an ethylene-α-olefinic copolymer rubber comprising 70 to 95 mol % ethylene units and 5 to 30 mol % α-olefin units.
U.S. Publication No. 2011/0160323 provides a process for forming a shaped article comprising: (a) forming a polymeric admixture comprise of at least one ethylene/α-olefin/non-conjugated diene interpolymer, at least one sulfur-based curative or organic peroxide-based crosslinking agent, and, optionally, a process oil, carbon blacks, additional inorganic fillers, organic fillers, cure accelerators, and/or foaming agents; (b) shaping the resulting admixture; and (c) heating the resulting admixture to a temperature at least the decomposition temperature of the sulfur-based cure agent or the peroxide crosslinking agent.
U.S. Publication No. 2011/0135909 relates to an EPDM foam obtained by foaming an ethylene-propylene-diene rubber, 0.1 to 5 parts by weight of a vulcanizer, 0.1 to 10 parts by weight of a vulcanization accelerator, 1 to 30 parts by weight of a foaming agent, and a foaming auxiliary agent.
As discussed above, there remains a need for EPDM-based compositions for manufacturing foamed profiles with reduced density while maintaining properties including compression set and compression load deflection at a level comparable to those of conventional EPDM foams, so as to provide desirable sealing performance of final automotive sealants made therefrom with reduced weight. Applicants have found that the above objectives can be achieved by blending a propylene-based elastomer with EPDM to prepare a foamed profile, which can be used for manufacturing automotive sealants. Applicants have also found that the addition of the propylene-based elastomer can reduce the use of the foaming agent without compromising the foaming effects, thus further lowering the cost for automotive sealants.